Many attempts have been made to improve the performance at the sealing surfaces of a rotary-type combustion engine. Typically, such an engine has a rotor defined with a number of circumferentially spaced apex portions having radially movable seal strips mounted within slots thereof for sealing engagement with the surrounding inner surface of the rotor housing. The rotor housing inner surface is typically of an epitrochoid configuration and is usually uninterrupted except for small ports defining areas for spark introduction admitting a fuel/air mixture or emitting exhaust.
Lubrication is essential to most engines for reducing wear at the contacting surfaces of the piston seal means and the cylinder walls. The lubrication problem in a piston engine is relatively simple in solution because of the reciprocating action of the piston which continuously bathes the cylinder walls with oil while preventing the oil from entering into the combustion zone of the engine. However, in a rotary combustion engine, the solution is not as simple since the oil becomes exposed to the combustion zone of the engine and will be consumed as it is introduced between apex seals and the inner surface of the rotor housing. The effectiveness of the oil as the lubricating film is rapidly reduced by the high operating temperatures in the rotary combustion engine. It has become known that due to the high temperatures and pressures at the mating sealing surfaces, and particularly the apex sealing surfaces, an oil film does not always satisfactorily prevent metal to metal contact which may result in a relatively rapid rate of wear at the metal contacting surfaces. This has been found to be a relatively serious problem during the break in period.
To provide apex seals without the need for oil, various types of wear-resistant materials have been tried. One group of such materials has been preferentially formed by compacting metal powders followed by sintering operations; various combinations of powdered aluminum with carbon have been used, iron-titanium carbide mixtures have been used, and also hot pressed silicon nitride. In addition, various types of alloys have been employed and tool steel has been impregnated with graphite and various types of unusually hard wear-resistant ceramic coatings have been applied by plasma or flame-spray techniques. The cost or performance of such materials have not been optimal because of the difficulty of finding an opposing material for the seal to compatibly engage and with the difficulty of inherently achieving both lubrication and wear resistance in a single material.
The seal means carried by the rotor are in constant rubbing engagement with the inner surfaces of the peripheral wall and end walls. As will be apparent, the constant relative rubbing engagement between the seal members and the inner surface can result in serious wearing problems of these elements and can ultimately terminate the useful life of the engine.
For example, one common solution to the compatibility problem has been to provide a liner of wear-resistant compatible material on the inner surface of the rotor housing. Such materials as hard chromium plated plating, or a carbide liner has been employed. But the use of liners or coatings has not been totally satisfactory because of non-uniform heat dissipation and gas loading characteristics of rotary combustion engines. There is resulting tendency for the liners to separate from the housing base material and in many cases the liners do not achieve the appropriate wear improvement sought.